However, some experts say that cycle helmets can actually increase the danger of head injury.

The theory is that that helmeted cyclists are lulled into a false sense of security and therefore take greater risks than their more vulnerable counterparts.

Independent researcher John Franklin analysed data in Australia, the first country to make cycle helmets compulsory.

He found that since the law was tightened head injuries had fallen by 11% - but there were 15% fewer cyclists on the roads, suggesting the risk has actually increased.

The British Medical Association is also concerned that making cycle helmets compulsory would put many people off cycling, and that the resulting lack of exercise would be more dangerous than the risk of head injuries.

A spokesman for the Royal Society for the Prevention of Accidents said: "We welcome this research.

"It confirms a lot of other research over the years that shows that wearing a cycle helmet can reduce the risk of receiving head and brain injuries.

"Rospa recommend that all cyclists wear an approved helmet whenever they cycle."

Helmets contain a thick layer of polystyrene which absorbs the force of an impact.

It is, however, important for the helmet to fit well so that it
stays in place during a fall, and the polystyrene layer can only be compressed once so helmets should be replaced after an accident.

The spokesman said that 173 cyclists were killed in road accidents in the UK last year.